Corrosion behavior of Ti‐xNb‐13Zr alloys in Ringer's solution

Ti‐6Al‐4V alloy has been widely used in restorative surgery due to its high corrosion resistance and biocompatibility. Nevertheless, some studies showed that V and Al release in the organism might induce cytotoxic effects and neurological disorders, which led to the development of V‐free alloys and both V‐ and Al‐free alloys containing Nb, Zr, Ta, or Mo. Among these alloys, Ti‐13Nb‐13Zr alloy is promising due to its better biomechanical compatibility than Ti‐6Al‐4V. In this work, the corrosion behavior of Ti, Ti‐6Al‐4V, and Ti‐xNb‐13Zr alloys (x = 5, 13, and 20) was evaluated in Ringer's solution (pH 7.5) at 37 °C through open‐circuit potential measurements, potentiodynamic polarization, and electrochemical impedance spectroscopy. Spontaneous passivity was observed for all materials in this medium. Low corrosion current densities (in the order of 10^?7 A/cm²) and high impedance values (in the order of 10⁵ Ωcm² at low frequencies) indicated their high corrosion resistance. EIS results showed that the passivating films were constituted of an outer porous layer (very low resistance) and an inner compact layer (high resistance), the latter providing the corrosion resistance of the materials. There was evidence that the Ti‐xNb‐13Zr alloys were more corrosion resistant than both Ti and Ti‐6Al‐4V in Ringer's solution.     

Corrosion inhibition of Ti‐6Al‐4V alloy in sulfuric and hydrochloric acid solutions using inorganic passivators

The effect of iodate (IO₃^?), metavanadata (VO₃^?) and molybdate (MoO₄^2?) anions on the passivation of Ti‐6Al‐4V alloy in sulfuric and hydrochloric acid solutions was studied using open‐circuit potential measurements, polarization techniques and electrochemical impedance spectroscopy (EIS). The alloy surface was examined by scanning electron microscopy (SEM). It was found that an optimum concentration of the passivator is essential for the corrosion inhibition process. Above this concentration the rate of alloy corrosion decreases as the concentration of the passivating ion increases. Scanning electron micrographs have shown that the flawed regions present in the alloy surface were repaired in the presence of the passivator anion. The optimum concentration of each anion and its corrosion inhibition efficiency for titanium and Ti‐6Al‐4V alloy have been determined. It turned out that the corrosion inhibition efficiencies of IO₃^?, VO₃^? and MoO₄^2? anions for the corrosion of Ti and Ti‐6Al‐4V in both hydrochloric and sulphuric acid solutions exceed 98%.     

Interface activation and surface characteristics of Ti/TiN/HA coated sintered stainless steels

Interface activation and surface characteristics of Ti/TiN/HA film coated sintered stainless steels (SSS) have been investigated by electrochemical and biocompatibility tests. HA (hydroxyapatite), Ti, and Ti/TiN film coatings were applied using electron-beam deposition method (EB-PVD). Ti, Ti/TiN, and Ti/TiN/HA film coated surfaces and layers were investigated by SEM and XPS. The coated films showed micro-columnar structure, and Ti/TiN/HA films were denser than Ti or HA-only film. The corrosion resistance of the HA coating was similar to that of Ti/TiN/HA film coating when Cu content reached 4 wt.%, but the corrosion resistance of the HA coating decreased when Cu content increased from 4 wt.% in 0.9% NaCl solution. Therefore, HA-only coating could ensure corrosion resistance when Cu content does not exceed 4 wt.%. The results of biocompatibility tests of SSS on dogs showed that bone formation and biocompatibility were favorable when Cu content did not exceed 4 wt.%. The biocompatibility with bone was generally favorable in Ti/TiN/HA film coating and HA-only coating, while bone formation was somewhat faster for the HA film coated surface than for the Ti/TiN/HA film coating. Also, good cell growth and osseointegration without toxicity were observed.     

钛合金表面GO/HA/MAO复合膜层的制备及其性能

为了改善钛合金种植体在体液中的腐蚀及摩擦腐蚀行为,延长其在人体环境中的服役时间,在微弧氧化 (MAO)膜层上采用溶胶凝胶(Sol-gel)法于羟基磷灰石(HA)和氧化石墨烯(GO)的混合溶胶中浸渍提拉成膜,从而在 Ti6Al4V 合金表面成功地制备了 GO/ HA/ MAO 复合膜层。 结果表明,MAO 膜层表面的微孔及微球被 GO/ HA 薄膜有效的覆盖且较为致密;膜层的物相组成主要为金红石相及锐钛矿相的 TiO₂、HA、SiO₂ 和GO;根据电化学腐蚀和摩擦腐蚀结果分析知,GO/ HA/ MAO 复合膜层在模拟体液(SBF)中的耐蚀性及耐摩擦腐蚀性相比于 MAO 膜层和 Ti6Al4V 基体均得到了显著提高。     

Corrosion behavior of polypyrrole/hydroxyapatite nanocomposite thin films electropolymerized on NiTi substrates in simulated body fluid

Hydroxyapatite (HAp) nanoparticles synthesized via microwave irradiation. Polypyrrole (PPy)/HAp nanocomposite was obtained using electropolymerization on nitinol (Ni) titanium (Ti) substrates. Fourier transform infrared was employed to characterize the nanocomposite formation. Electrochemical properties of the nanocomposite were investigated using polarization and electrochemical impedance spectroscopy (EIS) in simulated body fluid (SBF, 37 ± 0.1 °C). It was concluded that the NiTi specimen coated with PPy/HAp nanocomposite, has higher corrosion resistance than the NiTi coated with pure PPy in the SBF; however, NiTi was better than both coated NiTi. EIS results confirmed corrosion properties. Also, EIS was used to predict the morphology of the coatings. It predicted fine and compact morphology of the nanocomposite that was confirmed using scanning electron microscopy.     

Comparative study on corrosion protection properties of electroless Ni‐P‐ZrO2 and Ni‐P coatings on AZ91D magnesium alloy

Electroless Ni‐P‐ZrO₂ and Ni‐P coatings on AZ91D magnesium alloy were prepared, and their corrosion protection properties were compared in this paper. The potentiodynamic curves and electrochemical impedance spectroscopy (EIS) of the coated magnesium alloy in 3.5% NaCl solution showed that the corrosion performance of Ni‐P‐ZrO₂ composite coating was superior to that of Ni‐P coating. The same conclusion was obtained with salt spray and immersion tests. The corrosion morphologies of two kinds of coatings with various immersion time intervals in 3.5% NaCl solution indicated that most corrosion products concentrated on the nodules boundaries of Ni‐P coating and blocked corrosion pit was the main corrosion form. For the Ni‐P‐ZrO₂ coating, tortuous nodules boundaries were not the weak sites of the coating and corrosion initiated from the nickel phosphor alloy around the nanometer powders. Open corrosion pits occurred on the composite coating surface, and the coating was corroded gradually. Thus, the Ni‐P‐ZrO₂ coating exhibited better corrosion protection property to magnesium alloy substrate than Ni‐P coating.     

脉冲电化学沉积羟基磷灰石涂层改善Mg-Nd-Zn-Zr合金在模拟体液中的耐腐蚀性能

采用脉冲电化学沉积的方法,在新开发的Mg-Nd-Zn-Zr合金(JDBM)表面制备出了羟基磷灰石(HA)涂层,并对其耐蚀性能和血液相容性进行了研究.结果表明,表面改性后的JDBM镁合金具有更好的耐腐蚀性能,腐蚀后涂层保持了良好的完整性,析氢试验也表明涂层对基体在仿生腐蚀环境中有一定的保护作用,且不会引起模拟体液pH值较...     

Influence of fluoride concentration and pH on corrosion behavior of Ti‐6Al‐4V and Ti‐23Ta alloys in artificial saliva

Titanium alloys exhibit an excellent corrosion resistance in most aqueous media due to the formation of a stable oxide film and some of these alloys (particularly Ti‐6Al‐4V) were chosen for surgical and odontological implants for this resistance and their biocompatibility. Treatments with fluorides (F^?) are known as the main method to prevent plaque formation and dental caries. Toothpastes, mouthwashes and prophylactic gels can contain from 200 to 20 000 ppm F^? and can present neutral to acidic character, which can affect the corrosion behavior of titanium alloys devices present in the oral cavity. In this work, the behavior of Ti‐6Al‐4V and the new experimental Ti‐23Ta has been evaluated in artificial saliva of pH 2, 5 and 7 and different F^? concentrations (0, 1000, 5000 and 10 000 ppm), through open‐circuit potential measurements, potentiodynamic polarization and electrochemical impedance spectroscopy. A defined correlation between pH and F^? concentration settled the active or passive character of the materials. For both alloys, an active behavior was observed for pH 2 and 1000 to 10 000 ppm F^? and for pH 5 and 5000 and 10 000 ppm F^?. The passive behavior was observed for the other investigated conditions. The F^? concentration increase and pH decrease reduced the corrosion resistance of the alloys and decreased the stability of their passive film. The corrosion behavior of both alloys was very similar, but the Ti‐23Ta alloy generally presented slightly higher corrosion resistance.     

Biomimetic deposition of apatite coatings on micro-arc oxidation treated biomedical NiTi alloy

The biomedical NiTi alloy was treated by micro-arc oxidation in an electrolytes containing sodium aluminate and sodium hypophosphite at 400 V constant voltages for 30 min. The MAO-treated NiTi has a porous microstructure on its surface and coatings consisting only of the γ-Al₂O₃ phase. The ceramic coating prepared by micro-arc oxidation is composed of Al, Ti, Ni, O, and P with the atomic concentration of 26.98%, 3.67%, 3.33%, 65.30% and 0.72%, respectively. The MAO-treated NiTi was soaked in a simulated body fluid (1.0SBF) to investigate the biomimetic deposition of apatite on the surface of Al₂O₃ coated NiTi alloy. It was found that Al₂O₃ coated NiTi alloy shows an excellent apatite-forming ability after soaking in a simulated body fluid (1.0SBF) for 14 days, while no apatite-forming ability was observed on bared NiTi alloy even though soaking time is up to 28 days.     

The electrochemical behaviour of Ti‐13Nb‐13Zr alloy in various solutions

The electrochemical behaviour of a near‐β Ti‐13Nb‐13Zr alloy for the application as implants was investigated in various solutions. The electrolytes used were 0.9 wt% NaCl solution, Hanks' solution and a culture medium known as minimum essential medium (MEM) composed of salts, vitamins and amino acids, all at 37 °C. The electrochemical behaviour was investigated by the following electrochemical techniques: open circuit potential measurements as a function of time, electrochemical impedance spectroscopy (EIS) and determination of polarisation curves. The obtained results showed that the Ti alloy was passive in all electrolytes. The EIS results were analysed using an equivalent electrical circuit representing a duplex structure oxide layer, composed of an inner barrier layer, mainly responsible for the alloy corrosion resistance, and an outer and porous layer that has been associated to osteointegration ability. The properties of both layers were dependent on the electrolyte used. The results suggested that the thickest porous layer is formed in the MEM solution whereas the impedance of the barrier layer formed in this solution was the lowest among the electrolytes used. The polarisation curves showed a current increase at potentials around 1300 mV versus saturated calomel electrode (SCE), and this increase was also dependent on the electrolyte used. The highest increase in current density was also associated to the MEM solution suggesting that this is the most aggressive electrolyte to the Ti alloy among the three tested solutions.     

Improving wear resistance and corrosion resistance of AZ31 magnesium alloy by DLC/AlN/Al coating

A novel protective coating, consisting of three layers (top: diamond-like carbon, middle: aluminum nitride, bottom: aluminum), was deposited on the surface of AZ31 magnesium alloy layer by layer. Nano-indenter, electrochemical system and tribological tester were performed to investigate the hardness, wear resistance and corrosion resistance of the coated AZ31 magnesium alloy, respectively. The DLC/AlN/Al coating improved the magnesium alloy's surface hardness and reduced its friction coefficient, which consequently induced a great improvement of the magnesium alloy's wear resistance. Furthermore, the corrosion resistance of the AZ31 magnesium alloy with the DLC/AlN/Al coating was also enhanced with the corrosion current density decreasing from 2.25 × 10⁻⁵ A/cm² to 1.28 × 10⁻⁶ A/cm² in a 3.5 wt.% NaCl solution.     

Electrochemical characterization of Ni47.7Ti37.8Nb14.5 shape memory alloy in artificial saliva

Electrochemical corrosion behaviour of the studied Ni_47.7Ti_37.8Nb_14.5 (NiTiNb) shape memory alloy was investigated for dental applications. An equiatomic NiTi alloy was used in some tests as reference material. Electrochemical techniques such as anodic potentiodynamic polarization, open circuit potential and electrochemical impedance spectroscopy (EIS) were employed. Experiments were carried out using artificial saliva. Very low passive current densities were obtained from the anodic polarization curve, indicating a typical passive behaviour for NiTiNb alloy. Over the surface of the NiTiNb alloy uniform corrosion appears, while in case of the NiTi alloy surface pitting corrosion is developed. The role that Nb plays as an alloying element is by increasing the resistance of NiTi alloy to localized corrosion. The EIS results exhibited high impedance values (order of 10⁶ Ω cm²) obtained from medium to low frequencies which are indicative of the formation of a highly stable passive film on NiTiNb alloy in the artificial saliva.     

Influence of microstructural changes on corrosion behaviour of thermally aged Ti‐6Al‐7Nb alloy

Solution treatment and ageing (STA) is an effective strengthening method for α + β titanium alloys. This paper reports the effect of solution treatment and aging on the corrosion behaviour of Ti‐6Al‐7Nb alloy in a simulated body fluid (Ringer's solution). Ti‐6Al‐7Nb alloy is hot rolled in the α + β field and subjected to solution treatment above and below its beta transus temperature (1283 K). The solution treated specimens are water quenched (WQ), air‐cooled (AC), and furnace cooled (FC) at three different rates, and subsequently aged at 823 K for 4 h. Microstructural changes were examined using optical microscopy and phases developed were analyzed using XRD. The influence of microstructure on the corrosion performance of the alloys are discussed in detail based on the Open Circuit Potential (OCP), passive current density and area of repassivation loop values obtained from the cyclic polarization study in Ringer's solution. The passive current density was low (0.5 μA/cm²) for the specimen with duplex microstructure obtained for specimen solution treated at 1223 K, air‐cooled, and aged, in comparison with that for as‐rolled specimen (1.5 μA/cm²). The corrosion aspects resulting from various heat treatments are discussed in detail.     

Short and long term degradation behaviour of Mg–1Ca magnesium alloys and protective coatings based on plasma‐chemical oxidation and biodegradable polymer coating in synthetic body fluid

The main problem limiting the application of magnesium alloys as biodegradable implant material is its high degradation rate. In order to slow down the corrosion rate an extrusion process and specific coating systems based on plasma‐chemical oxidation (PCO) and organic dip coating with poly(L ‐lactid‐co‐caprolacton) (PLLC) were applied on Mg–1Ca magnesium alloy. The additional PLLC coating is used to delay the start of substrate corrosion, while the purpose of the PCO coating is to decrease the substrate corrosion rate. The corrosion behaviour was investigated in synthetic body fluid (SBF) through measurement of the hydrogen evolution rate in long term tests and polarisation and electrochemical noise measurements in short term tests. The results showed significant differences between the cast and extruded alloys and a decrease of the corrosion rate due to corrosion product formation. The combination of both coating systems resulted in a significant delay of metal substrate corrosion and all coating systems showed good correlation between short and long term tests. The combination of the three investigation methods provides the possibility to gain more information about the degradation behaviour and break down of protective coatings.     

NiTi合金激光熔凝处理及其生物腐蚀性能研究

目的 通过对NiTi合金表面进行激光熔凝处理,从而提高NiTi合金的耐腐蚀性能。方法 利用紫外激光器对NiTi合金进行表面熔凝处理,借助扫描电子显微镜(SEM)、光学显微镜(OM)、能量色散X射线光谱仪(EDX)和X射线衍射仪(XRD)等技术手段,研究了激光熔凝处理前后NiTi合金的表面显微组织、成分和相结构。测试了激光熔凝处理前后NiTi合金表面与模拟体液(SBF)的接触角、熔凝层的显微硬度等表面性能。通过全浸腐蚀试验和电化学测试,研究了熔凝层在SBF溶液中的生物腐蚀性能,并分析了腐蚀机理。结果 NiTi合金经过激光熔凝处理后,在合金的表层形成了厚度为90~150 μm的熔凝层,熔凝层主要由TiO2、β相以及少量的TiO相组成。合金表面的平均显微硬度提高了153~279HV,合金的表面接触角增大,由亲水性转为疏水性。相较于未处理的样品,熔凝处理后的样品在SBF溶液中的腐蚀电位分别正移了435 mV和413 mV,腐蚀电流密度分别下降了83%、62%左右。熔凝处理后的样品在SBF溶液浸泡168 h后,SBF溶液中的Ni²⁺浓度下降了约1/3。结论 以适当的激光加工参数对NiTi合金进行激光熔凝处理,可在NiTi合金表面形成致密的氧化膜,这层氧化膜和熔凝层可以有效地抑制NiTi合金在SBF溶液中的点腐蚀行为。     

Corrosion performance and tribological behavior of diamond-like carbon based coating applied on Ni−Al−bronze alloy

The effect of diamond-like carbon (DLC) coating (fabricated by cathodic arc deposition) on mechanical properties, tribological behavior and corrosion performance of the Ni?Al?bronze (NAB) alloy was investigated. Nano-hardness and pin-on-plate test showed that DLC coating had a greater hardness compared with NAB alloy. Besides, the decrease in friction coefficient from 0.2 for NAB substrate to 0.13 for the DLC-coated sample was observed. Potentiodynamic polarization and EIS results showed that the corrosion current density decreased from 2.5 μA/cm² for bare NAB alloy to 0.14 μA/cm² for DLC-coated sample in 3.5 wt.% NaCl solution. Moreover, the charge transfer resistance at the substrate–electrolyte interface increased from 3.3 kΩ·cm² for NAB alloy to 120.8 kΩ·cm² for DLC-coated alloy, which indicated an increase in corrosion resistance due to the DLC coating.     

镁合金直接化学镀Ni-B镀层的腐蚀电化学行为研究

  研究了镁合金表面化学镀Ni-B合金的电化学行为,采用电化学动电位扫描极化曲线和交流阻抗研究了Ni-B镀层的腐蚀电化学行为,结果表明,Ni-B镀层在3.5%NaCl溶液中具有优良的耐蚀性能.所得Ni-B镀层的自腐蚀电位在－400 mV左右,相对于基体-1460 mV提高了1000 mV,自腐蚀电流密度小于0.7 μA/cm²,相对于基体28.5 μA/cm²降低了近两个数量级,说明Ni-B镀层能够有效地提高AZ91D 镁合金的耐腐蚀性能,使AZ91D镁合金在35%NaCl溶液腐蚀介质中的腐蚀速度明显降低.电化学交流阻抗测试结果符合极化曲线的测量结果,化学镀Ni B镀层后的AZ91D镁合金在3.5％NaCl溶液中的阻抗值相对于基体提高两个数量级,表现为自腐蚀电流降低,阻抗值相应提高.     

Effect of Surface Alloying by Silicon on the Corrosion Resistance and Biocompatibility of the Binary NiTi

This paper presents the study on changes in element and phase compositions in the near-surface layer and on surface topography of the NiTi specimens after the silicon ion-beam treatment. The effect of these parameters of the near-surface layer on corrosion properties in biochemical solutions and biocompatibility with mesenchymal stem cells of rat marrow is studied. Ion-beam surface modification of the specimens was performed by a DIANA-3 implanter (Tomsk, Russia), using single-ion-beam pulses under oil-free pumping and high vacuum (10^?4 Pa) conditions in a high-dose ion implantation regime. The fluence made 2 × 10¹⁷ cm^?2, at an average accelerating voltage of 60 kV, and pulse repetition frequency of 50 Hz. The silicon ion-beam treatment of specimen surfaces is shown to bring about a nearly twofold improvement in the corrosion resistance of the material to attack by aqueous solutions of NaCl (artificial body fluid) and human plasma and a drastic decrease in the nickel concentration after immersion of the specimens into the solutions for ~3400 and ~6000 h, respectively (for the artificial plasma solution, a nearly 20-fold decrease in the Ni concentration is observed). It is shown that improvement of NiTi corrosion resistance after treatment by Si ions occurs mainly due to the formation of two-layer composite coating based on Ti oxides (outer layer) on the NiTi surface and adjacent inner layer of oxides, carbides, and silicides of the NiTi alloy components. Inner layer with high silicon concentration serves as a barrier layer preventing nickel penetration into biomedium. This, in our opinion, is the main reason why the NiTi alloy exhibits no cytotoxic properties after ion modification of its surface and leads to the biocompatibility improvement at the cellular level, respectively.     

氟处理对AZ31B镁合金生物耐蚀降解行为的影响

采用低温化学方法在AZ31B镁合金表面制备出氟涂层,并研究了涂层的表面特征,氟处理后AZ31B镁合金在模拟体液中的腐蚀行为。结果表明,氟涂层均匀致密,与基体结合良好。经氟处理后的AZ31B镁合金的耐蚀性能有较大提高,其在模拟体液中的降解缓慢,合金浸泡后溶液的pH值保持在7.5~8.8之间,有效降低了合金降解而引起的碱性增强趋势。氟涂层在模拟体液中会逐渐转化为Ca3(PO4)2,新生成的表面膜会继续起到保护合金基体的作用。     

Corrosion characterization of microarc oxidation coatings formed on Mg–7Li alloy

Ceramic coatings with thickness of 27 µm were fabricated on Mg–7Li alloy in Na₂SiO₃–C₆H₁₈O₂₄P₆ solution by microarc oxidation (MAO). The morphology and phase composition of MAO coatings were characterized by scanning electron microscopy (SEM) and X‐ray diffraction (XRD). The corrosion behavior of the bare and MAO coated Mg–7Li alloy was investigated by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). Results showed that the MAO coatings were composed of MgO, Li₂O, and Mg₂SiO₄, and there existed some micropores on the coating surface with a diameter of 3–20 µm. The corrosion potential (E_corr) and corrosion current density (I_corr) of the MAO coated alloy were about ?1.4761 V and 7.204 × 10^?7 A/cm², respectively. The E_corr of the MAO coated alloy increased by 109.6 mV and its I_corr decreased by three orders compared with that of the bare Mg–7Li alloy. The EIS plots indicated that the impedance of the MAO coated alloy was 15 times higher than that of the bare alloy. The fitting parameters showed that the resistance of the MAO coatings was far greater than that of the bare alloy. The dense intermediate layer and the transition layer of the MAO coatings acted as a barrier to hinder the proceeding of solution permeation, remarkably improving the corrosion resistance of the Mg–7Li alloy.